Method and apparatus for examining food products by means of irradiation
BACKGROUND OF THE INVENTION 
     The invention relates to a method for examining food products such as meat to detect undesired ingredients, such as bone fragments, by means of irradiation. 
     In consequence to the increased demand for a larger assortment of food products, such as meat, fish and poultry, increasing automation has occurred in the respective sectors of the industry. With such an automation, of which an example is the mechanical filleting of chickens, a higher production capacity is obtained than would be the case without automation. However, a disadvantage of such automation is that a final check of the food product is required, for example, to determine the presence of bone fragments or the like. 
     A known method for examining food products by means of irradiation uses X-rays. However, large scale use of X-rays for examining food products is commercially unattractive, for the consumer does not like to buy food products which have been treated with X-rays. An indication on the final product that has been examined, using X-rays, would have very negative consequences on the commercial success of such a food product. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a method for examining food products by means of irradiation, which does not have this disadvantage and is not thought of in a negative way by the consumer. 
     The method according to the invention, is characterized in that a laser beam is used for the irradiation which scans the food product according to a predetermined pattern and, wherein, the local intensity of the laser beam passing through the food product is determined for detecting undesired ingredients. 
     The application of a laser beam for the irradiation of food products has absolutely no hazards for the public health. Further, a laser beam penetrates food products such as meat, fish and the like wall. The determined local intensity of the laser beam passing through the food product is substantially proportional with the density of the meat or the undesired ingredients contained therein, such that determined variations in the intensity represent a direct indication of undesired ingredients in the food product. By feeding the determined local intensity value to a computer, which takes into account the specific wave length of the laser beam, the substance of the food product as well as the substance of expected ingredients (bone, cartilage, fishbones or the like), can be determined, and undesired ingredients present in the food product can be identified. 
     According to a preferred embodiment of the method, according to the invention, the laser beams scans the food product on a line-by-line basis. 
     By means of such a line-by-line scan the computer creates an image of the local intensity variations, so that a picture is created of the undesired ingredients present. 
     According to another preferred embodiment of the method, according to the invention, the laser beam moves to and fro along the food product, while the food product is moved over a short distance, perpendicularly to the direction of motion of the laser beam, whenever the laser beam is in or near one of its outermost positions. 
     By combining of the to and fro movement of the laser beam and the stepwise advancement of the food product, the food product is scanned entirely, line-by-line. 
     The invention further relates to an apparatus for carrying out the method according to the invention. This apparatus comprises a laser means for moving the laser beam to and fro along the food product as well as detection means for determining the intensity of the laser beam passing through the food product. 
     A preferred embodiment of the apparatus, according to the invention, comprises a conveyor for the food product as well as two curved parabolic mirrors, respectively positioned above and below the conveyor. The parabolic axes of the mirrors extend in parallel to each other and substantially perpendicularly to the plane of motion of the conveyor, wherein the laser is positioned such that the laser beam is movable to and fro along the surface of one of the parabolic mirrors. However, the laser beam always originates from the focus of this parabolic mirror, and the detection means is positioned in the focus of the other parabolic mirror, wherein the conveyor near to the plane of the laser beam is transmissible for the laser beam. 
     This position of the parabolic mirrors and the position of the laser and the detection means make it possible for one laser beam to cover a plane which intersects the food product to be examined. In this way, it is possible to carry out a line-by-line scan of the food product. 
     It is advantageous if, according to a further embodiment of the invention, the laser is stationary and directed so that the laser beam hits a mirror positioned in the focus of one parabolic mirror, which is pivotable, to and fro. In this way the laser beam is moved to and fro over the surface of the one parabolic mirror while the laser itself is stationary. 
     If the conveyor comprises at least two conveyor belts, adjoining each other with a gap between them at the scanning plane of the laser beam, the food product can be moved through the apparatus without the conveyors presenting an obstruction for the laser beam. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Hereafter the invention will be described by means of the drawings in which an embodiment of the apparatus according to the invention is illustrated. 
     FIG. 1 is a perspective view of an embodiment of the apparatus according to the invention; and 
     FIG. 2 illustrates the operational principle of the apparatus according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The apparatus shown in FIG. 1 comprises a conveyor means for the food product to be examined comprising two conveyor belts 1, 2. Conveyor belts 1, 2 are aligned and have a gap 3 between them. 
     Above and below the conveyor means oppositely curved parabolic mirrors 4 and 5 are positioned. The position of both parabolic mirrors 4, 5 is such that their parabolic axes extend mutually in parallel and substantially perpendicularly to the plane of motion of the conveyors 1, 2. 
     A mirror 6 is positioned in the focus of the lower parabolic mirror 5, which, in a way not shown further, is pivotable to and fro about a pivot axis 7. A detection means 8 is positioned in the focus of the upper parabolic mirror. 
     Moreover, FIG. 1 shows that the apparatus further comprises a laser 9 which is directed so that the emitted laser beam 10 hits the pivotable mirror 6 substantially in its pivot axis 7. The laser 9 is in a stationary position. 
     In FIG. 2, several parts of the apparatus according to the invention are visible. Conveyors 1 and 2, upper and lower parabolic mirrors 4 and 5, respectively, mirror 6, pivotable about pivot axis 7, detection means 8, and laser 9. Laser beam 10, which originates from the laser 9, hits the mirror 6 substantially in its pivot axis 7. Moreover, in FIG. 2 a food product 11 to be examined is represented, in which an undesired ingredient, for example, a bone fragment 12, is contained. 
     As noted before, the laser beam 10 hits the pivotable mirror 6. Depending on the present position of the mirror 6 the reflected laser beam will hit the lower parabolic mirror 5 at different locations. In FIG. 2 this is indicated for a number of different locations by means of reflected laser beams 13-16. Since the mirror 6 is positioned in the focus of the lower parabolic mirror 5, the reflected laser beams 13-16 will, after hitting this parabolic mirror 5, be directed in parallel with each other, in the present case in a vertical plane. 
     Simultaneously the reflected laser beams 13-16 penetrate, depending on their position, the food product 11. In the represented position reflected laser beam 15 hits the bone fragment 12 in the food product 11. 
     The reflected laser beams 13-16 hit the upper parabolic mirror 4 and are focused on the detection means 8, positioned in the focus of parabolic mirror 4. In the present case this detection means 8 is a light sensitive element. 
     The intensity variations of the incoming laser beams (dependent on the density of the respective food product portion through which the laser beam penetrates) as determined by the detection means 8 are processed by a processing unit 17 which is connected to the detection means 8, so that an indication 18 is obtained of the presence of undesired ingredients. During this processing by means of the processing unit 17 the conveying velocity of the conveyors 1, 2 and the motion of the mirror 6 are taken into account. In this way one can determine which measured intensity belongs to what section of the food product to be examined. 
     Although the invention is explained above by means of an apparatus using two parabolic mirrors, it is possible to also choose a configuration which operates without parabolic mirrors. It is only essential that the laser beam is applied to scan the food product according to a predetermined pattern, and that the intensity of the laser beam passing through the food product is determined for detecting the undesired ingredients. 
     The invention is not limited to the embodiment described and can be varied widely within the scope of the invention.